Field of the Invention
The present invention relates to a method of manufacturing a light scanning apparatus that is used in an image forming apparatus such as a copier, a printer and a facsimile; and the image forming apparatus.
Description of the Related Art
An image forming apparatus that forms an image includes a light scanning apparatus which exposes a photosensitive member to light. The light scanning apparatus deflects a laser light emitted from a laser light source by a rotary polygon mirror provided in the inside, further changes the optical path of the deflected laser light to a direction of a photosensitive member by a reflection mirror, and thereby exposes the photosensitive member to light to form a latent image. The reflection mirror is a small member having a slim shape in order to save a space and reduce a cost of an optical element, because laser beams fly over in the light scanning apparatus. The reflection mirror is placed in a mirror supporting portion provided inside the housing of the light scanning apparatus, and is fixed to the mirror supporting portion by an elastic member. FIGS. 9A, 9B and 9C are schematic views for describing a support structure of a general reflection mirror 162. In FIG. 9B, such a structure is adopted that an elastic member 172 presses the reflection mirror 162 toward the mirror supporting portions 170 and 171 to fix the reflection mirror 162. FIG. 9A illustrates the mirror supporting portions 170 and 171 in such a state that the reflection mirror 162 is removed; and FIG. 9B illustrates a state in which the reflection mirror 162 is placed on the mirror supporting portions 170 and 171. In addition, FIG. 9C is a perspective view illustrating the shape of the elastic member 172 which fixes the reflection mirror 162 to the mirror supporting portions 170 and 171. As is illustrated in FIG. 9A, usually, the mirror supporting portions 170 and 171 are provided in the vicinity of both ends of the reflection mirror 162 in the longitudinal direction. As is illustrated in FIG. 9B, the bottom face side of the reflection mirror 162 is supported by the two mirror supporting portions 171, and the back face portion of the reflection surface of the reflection mirror 162 is supported by the mirror supporting portion 170. Incidentally, the back face side of the reflection surface of the reflection mirror 162 is supported by one seating surface 170a of the mirror supporting portion 170 provided on the left side in FIG. 9A, and by two seating surfaces 170b of the mirror supporting portion 170 provided on the right side.
The image forming apparatus not only has the light scanning apparatus, but also in the vicinity, has movable portions such as a paper conveying roller which conveys paper, a photosensitive member and an intermediate transfer body of an image forming portion, a fixing belt and rollers; and a driving system which drives the movable portions, provided therein. When a print job is executed, there is a possibility that the driving system such as a motor which drives these movable portions works, vibration generated by the driving system propagates also to the light scanning apparatus through the movable portions, and that the reflection mirror 162 vibrates. When the reflection mirror 162 vibrates, the direction of the laser light reflected by the reflection mirror 162 ends up changing along with the vibration of the reflection mirror 162, the imaging position on the photosensitive drum ends up deviating from the original position, and image unevenness such as a stripe pattern occasionally occurs on an image to be formed. Then, it has been investigated to shift a frequency of the vibration generated by the driving system and a resonance frequency with the reflection mirror 162, by such countermeasures as to attach a vibration damping member to the reflection mirror 162, partially apply a pressing force by an elastic member, or bond a part thereof. Japanese Patent Application Laid-Open No. 2014-209161, for instance, proposes such a structure as to be capable of moving a mirror supporting seating surface which supports a bottom face portion perpendicular to a reflection surface of the reflection mirror, in a longitudinal direction of the reflection mirror. According to this structure, the natural frequency of the reflection mirror can be shifted from a frequency of the vibration propagating from the movable portions of the image forming apparatus in such a state that the reflection mirror is placed in the housing of the light scanning apparatus, and the resonance of the reflection mirror can be suppressed.
However, in the case where the reflection mirror is fixed by being combined with a plurality of members as in the above described conventional technology, the natural frequency of the reflection mirror is affected by a boundary condition concerning the support of the reflection mirror and the structural stability in the vicinity of the seating surface which supports the member. As shown in Japanese Patent Application Laid-Open No. 2014-209161, in the case where the fixed seating surface of the reflection mirror is formed of a member different from the housing, and the fixed seating surface is fastened to the housing, such an operation becomes necessary as to move and adjust the fixed seating surface, and then fix the fixed seating surface to the housing. By the seating surface being fixed to the housing after the adjustment, the circumstance of the fastening structure changes, and the natural frequency of the reflection mirror ends up changing. In other words, even though the natural frequency of the reflection mirror is changed to a predetermined frequency by moving a position of the seating surface, there may be a case in which the vibration frequency ends up deviating from the predetermined frequency due to the fixing operation. As a result, a problem arises that a frequency of the vibration generated by a plurality of driving sources in the image forming apparatus coincides with the natural frequency of the reflection mirror, the reflection mirror largely vibrates, and simultaneously the image ends up deteriorating.
In recent years, there are many forms in which one light scanning apparatus copes with a plurality of resolutions and a plurality of printing speeds. Because of this, in order to configure the natural frequency of the reflection mirror so as not to coincide with the frequency of the vibration generated by the driving source and not to cause the resonance, by such countermeasures as to shift the position of the reflection mirror supporting seating surface, it is necessary to control the natural frequency of the member with high accuracy and always adjust the natural frequency to the predetermined frequency. Because of this, it becomes a problem that the supporting boundary condition of the member which supports the reflection mirror and the structure in the vicinity of the seating surface which supports the reflection mirror can be stably controlled.